The anemone won't be an issue at all. My Clarkii pair lays their eggs right next to their Haddoni, which will sometime cover the eggs.
As far as the water change, should be fine. But, if this is their first time spawning I wouldn't do a water change during it -- the spawn that is.
Mine have been spawning for 6+ years now, and I can do anything to the tank while they are laying eggs. It doesn't phase them at all now.